Presence and characterization of the human pathogenic Vibrio species in the microbiota of Manila clams using cultural and molecular methods

The North Adriatic lagoons and the Po River Delta are important areas for farming Manila clams (Ruditapes philippinarum). These areas have been heavily impacted by climate change, reducing livestock numbers and increasing pathogen spread. Shellfish, particularly clams, are primary vectors for Vibrio pathogens affecting humans. In this study, the occurrence of human pathogenic Vibrio species on Manila clams was investigated using an integrated approach that combined culture-dependent and culture-independent techniques. Samples were collected over three years from farming areas in the northeastern Adriatic lagoons and the Po River Delta, regions seriously impacted by climate change and pollution. In this study, species of the human pathogen Vibrio were analyzed in the clam microbiota and characterized using recA-pyrH metabarcoding and shotgun metagenomics. Human pathogenic Vibrio species were widespread in the clam microbiota, especially in summer, demonstrating that the environmental conditions on the northern Adriatic coasts allowed the growth of these bacteria. V. parahaemolyticus and V. vulnificus were also quantified using qPCR in <50 % of summer samples Shotgun metagenomics revealed the similarity of V. parahaemolyticus strains to other worldwide genomes, enabling improved pathogen identification and tracking. In the future, climate change could cause these conditions to become even more favorable to these bacteria, potentially increasing pathogen spread. Consequently, enhanced monitoring and control of both the environment and seafood products should be planned to ensure food safety.